1. Field of the Invention
This invention relates to light emitting devices, such as light emitting devices comprising phosphor translucent ceramics.
2. Description of the Related Art
White light-emitting devices may be fabricated using a combination of a blue light-emitting diode (LED) and a phosphor material. These devices are often configured so that the blue light from the blue light-emitting diode comes in contact with the phosphor material so that the phosphor material may absorb a portion of the blue light and emit light that is of a longer wavelength. As a result, these materials have been described as wavelength converting or color changing materials. This allows the device to emit a combination of light that appears more white. There are two common methods for doing so. First, the phosphor particles may be dispersed in another solid component, for example, an encapsulent resin, through which the light passes, thus coming into contact with the dispersed phosphor particles. Second, the phosphor material may be in the form of a phosphor ceramic compact, in which case the blue light would pass through the compact.
The disadvantage of the phosphor particles is that particles that are large enough to be emissive have a tendency to scatter the light, thus reducing the white light emission of the device. On the other hand, the phosphor ceramic compacts are generally prepared by annealing of the phosphor powder and subsequent sintering of the compact, which condition can affect the luminescent efficiency of the phosphor ceramic. Luminescence efficiency can be improved by annealing the phosphor ceramic compacts under a reducing atmosphere, but that tends to make the compacts more opaque, thus reducing the utility of the light-emitting device. Thus, there is a need for a translucent phosphor ceramic compact with improved luminescence.